Electromagnet for blood flowmeters and the like

ABSTRACT

An improved electromagnet for blood flowmeters and the like is made by filling the open central portion of a magnetizing coil with a mixture of iron powder suspended in a quick-hardening epoxy resin. The mixture is thereafter heated and cured to form an electrically nonconductive magnetic core.

[ 51 3,636,764 51 Jan. ,2 5, 1972 United States Patent Funfstuck Lochneret [54] ELECTROMAGNET FOR BLOOD FLOWMETERS AND THE LIKE 3/1967Kolineta1................'.........

5/1967 Westersten l [72] Inventor: Horst Funistuck, Los Angeles, Calif.

Statham Instruments, Inc

Oct. 30, 1969 Wada................................73/l94 EM Oxnard,Calif.

[73] Assignee:

[22] Filed:

OTHER PUBLICATIONS Biotronex Laboratory, Inc.; FlowTransducers-Information and Price List P 700; Feb. 15, 1967 Appl. No.:872,688

Paul L. Gardner and Kendrick and n m M A m S C B fl A 0 k b u "S mu mm xi. .WCW am w mo H it I! 5 PAS 11 38 5 31 n l /5 22 0.5 W 3 5 02H1 Pow 5m m7 M W0 w 2 2 6 4 6 M 5 2 3 E "m; 9 "9 n .2.E 3 m m m W nu, u 3 n 7 mmM mmn9 m m& f W d S M U.mF .111. 2 8 555 [[1 Rehrenm Cited An improvedelectromagnet for blood flowmeters and the like is made by filling theopen central portion of a magnetizing coil with a mixture of iron powdersuspended in a quick- UNITED STATES PATENTS m SW1; rm 3 m a 4 me um w. hm, RMWSm d n s df w w wk m n m8 a m e m "we h.w. m- I F 8 mm .m C W .m mn mn D MIN 4. 3 S 1 1 m" n" 1, I Ch C we 3 Km Wm Cf 00 m .mo n ed de uIf au hc XXXX. 838MB 030 H 626M II/EH 969 232 m .1 n/ 3 7;

ELECTROMAGNET FOR BLOOD FLOWMETERS AND THELIKE BACKGROUND OF THEINVENTION The present invention relates to an improved electromagnet,particularly suited for use in a blood flowmeter or the like, and animproved process for manufacturing the same.

One currently popular technique for determining the quantity of bloodflowing through a blood vessel is by applying a magnetic field acrossthe vessel to induce an electric signal in the blood, and thereaftermeasuring the magnitude of the signal by spaced electrodes which contactthe outer surface of the vessel. The magnitude of the measured signal isdirectly related to the velocity of the blood flowing through thevessel, from which the quantity of blood flowing may be determined.

Suitable instruments for carrying out the above technique are shown, forexample, in U.S. Pat. No. 3,316,762, and copending U.S. Pat. applicationSer. No. 802,517, now U.S. Pat. No. 3,580,071. Such an instrumenttypically comprises an insulative hollow cylindrical tube adapted to fitaround a blood vessel under test, one or more magnets mounted on theexterior of the tube, and a pair of spaced electrodes connected to asuitable signal measuring apparatus for measuring the magnitude of theelectric signal induced in the blood by the electromagnets.

While both coreless field magnets and electromagnets having iron coreshave been employed to induce the electric signal in the blood,electromagnets employing iron cores provide concentrated magneticfields, thereby improving the performance of their instruments,increasing their efficiency and decreasing their required size. However,such electromagnets have heretofore been subject to severaldisadvantages. The

iron cores are commonly made of transformer lamination material, ferriteor-iron oxide. These materials are rigid and relatively difficult tomachine or-shape, and the cores must be machined to precisely fit thecoils and the exterior surfaces of the tubes on which they are mounted.As a result, an electromagnet with a properly fitting core hasheretofore been expensive and difficult to manufacture.

Another problem heretofore associated with instruments employingelectromagnets having solid iron cores is that such cores areelectrically conductive, and introduce eddy current effects into theirsystems. Such eddy current effects generate artifact voltages whichresult in baseline instability in the signal measuring apparatus.

SUMMARY OF THE INVENTION In view of the foregoing, it is an object ofthe present invention to provide an improved electromagnet, particularlysuited for use in blood flowmeters and the like which employs an ironcore that fits its coil exactly, introduces minimal'eddy current effectsand capacitive coupling into its system, produces no electrical shorts,and yet is relatively inexpensive to manufacture. It is a further objectof this invention to provide an improved process for manufacturing suchan electromagnet.

The foregoing and other objects have been realized by theimprovedelectromagnet of the present invention, which is manufactured by fillingthe open central portion of a coil with a generally viscous mixture offerromagnetic particles (e.g., iron powder) suspended in a relativelyquick-hardening resin. Thereafter, the viscous mixture is heated andcured to form a solid, electrically nonconductive magnetic core.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1V is a perspective viewillustrating one of the initial steps in making a blood flowmeteraccording to the teachings of the present invention, i.e., mounting amagnetizing coil on the exterior surface of a cylindrical tube which isadapted to fit around a blood vessel to be tested;

FIG. 2 is a perspective view schematically illustrating another of thesteps in the process of the present invention, i.e., mixing a quantityof iron powder with an epoxy resin and a suitable hardening catalyst toform a viscous mixture which will subsequently harden into a solid,electrically nonconductive, magnetic'core;

FIG. 3 is a sectional end elevation view showing the viscous mixture ofiron powder and epoxy resin being packed into the open central portionof one of the 'coils mounted on the cylindrical tube; and

FIG. 4 is a sectional view taken along the line 4-4 of FIG. 3, showingthe manner in which the viscous mixture of iron powder and epoxy resincompletely fills the central portion of the coil inwhich it is packedand conforms precisely to the shape of the interior wall of the coil.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT The first step in makinga blood flowmeter according to the process of the present invention isto wind a wire of conductive material around a suitable mandrel (notshown) to form a magnetizing coil 10 which is adapted to be mounted onthe exterior surface of a hollow cylindrical tube 12. As best shown inFIGS. 1 and 3, the coil has an open central portion 14 and is generallyarcuate in shape so that it will conform to the exterior surface of thetube 12. The mandrel on which the coil 10 is wound should be so designedthat the coil 10 wound thereon will assume the configuration shown inthe drawings. Preferably, the mandrel is made of a soft, smooth materialso that it will not cut into the insulation around the coil windings.Leads 16, 18 from the coil 10 are adapted to be connected to a suitablesource of AC power (not shown). 7

After the coil 10 has been wound, it is removed from the mandrel andglued or otherwise suitably mounted on the exterior surface of a hollowcylindrical tube or lumen 12. The tube 12 is adapted to receive a bloodvessel to be tested, and is made of an electrically insulative material.For the reasons set forth in copending U.S. application Ser. No.802,517, it may be desirable to mount two coils 10, 10 on the tube 12,as shown in FIG. 3.

After the coil or coils l0, 10 have been mounted on the tube 12, thecentral portion 14 thereof may be packed with a liquid mixture 20 ofrelatively high viscosity which will harden into a solid, electricallynonconductive, magnetic core. As shown in FIG. 2, the viscous mixture 20is formed by mixing a measured quantity of particulate ferromagneticmaterial, such as highpermeability iron powder 22, with a measuredquantity of epoxy resin 24 and a suitable catalyst 26 which will causethe mixture to harden relatively quickly. Of course, ferromagneticmaterials other than iron (e.g., cobalt, nickel, etc., and mix turesthereof) may be effectively employed.

The concentration of iron powder 22 in the mixture 20 must be sufficientto render the finished electromagnet capable-of establishing the desireddegree of magnetic flux; and the mixture 20 must be of sufficientfluidity to be readily packed into the central portion 14 of the coil10.

By way of example, the viscous substance 20 may be formed by mixing 10grams of epoxy resin (e.g., Shell Chemical Corporation 0828) with 44grams of iron powder (e.g., 0Ancor EP 1024, from I-IoeganeasCorporation, Riverton, N.J.), and thereafter mixing 3.2 grams of theiron powder-epoxy resin mixture with I drop .(about 0.03 gram) of ahardening catalyst (e.g., 09 from Emerson Cuming, Inc.).

The viscous mixture 20 is then packed into the open center portion 14 ofthe coil 10, as shown in FIG. 3, so as to conform to and be in intimateand continuous contact with the interior wall of the coil 10 and aportion of the exterior surface of the tube or lumen 12. The mixture isthen heated by suitable means (e. g., a lamp) for a suitable period oftime (e.g., 1 minute), and thereafier cured.

Curing of the mixture may be effected by letting the packed coil set atroom temperature for a suitable period of time (e.g., 24 hours).Alternatively, the curing step may be accelerated by placing the packedcoil in an oven (e.g., at F.) for a suitable period of time (e.g., 1hour).

The finished core 20 (FIG. 4) is an electrically nonconductive, magneticsolid.

From the foregoing, it will be readily appreciated that the finished'core 20, having been packed into the open central portion 14 of thecoil while of a viscous or pasty consistency, will precisely fit theinterior wall of the coil 10 and the exterior surface of the lumen 12,as shown in FIG. 4. Since no machining or cutting of the core isrequired, the cost of making the electromagnet (coil 10 and core 20) isrelatively inexpensive.

Since the finished core is an electrically nonconductive magneticmaterial, no electrical shorts will be produced between the coilwindings and the core. Moreover, only minimal eddy current effects andcapacitive coupling will be introduced.

Still another advantage realized by an electromagnet manufacturedaccording to the process described above over electromagnets whichemploy a machined iron core, is an increase of approximately 20 percentin the magnetic intensity of the electromagnet. This increase isattributed to the fact that the substance 20 which hardens into thefinished core is packed into the coil 10 while in a viscous condition,and thereby fills substantially all of the voids in the interior wall ofthe coil.

1 claim:

1. An improved blood fiowmeter comprising:

an insulative hollow cylindrical tube adapted to fit around a bloodvessel;

an electromagnet mounted on said tube for applying a magv ing to andbeing in intimate and continuous contact with said interior wall of saidcoil and a portion of the exterior surface of said tube; said corecomprising a hardened resin having ferromagnetic particlessuspendedtherein; and signal measuring means operatively connected tosaid tube for measuring the magnitude of the electric signal induced inthe blood flowing through the blood vessel. 2. A blood fiowmeter inwhich a magnetic field is induced in a blood vessel by means of anelectromagnet to induce an electrical signal when blood flows throughsaid blood vessel, the improvement which comprises a hollow cylindricaltube adapted to fit around the blood vessel, an electromagnet mounted onsaid tube, for applying a magnetic field across said tube, saidelectromagnet comprising an electrically conductive coil having aninterior wall defining an open central portion; and an electricallynonconductive magnetic core substantially filling said open centralportion of said coil, and conforming to and being in intimate andcontinuous contact with said interior wall of said coil, said corecomprising a resin having therethrough magnetic particles suspendedtherein.

3. A lumen for a blood flowmeter, said lumen comprising an insulatedhollow cylindrical tube adapted to fit around a blood vessel, anelectromagnet mounted on said tube to apply a magnetic field across saidtube, said electromagnet comprising an electrically conductive coilhaving an interior wall defining an open central portion and anelectrically nonconductive magnetic core substantially filling said opencentral portion of said coil and conforming to and being in intimate andcontinuous contact with said interior wall of said coil, said corecomprising a hardened resin with magnetic particles suspended therein.

H k l i

1. An improved blood flowmeter comprising: an insulative hollow cylindrical tube adapted to fit around a blood vessel; an electromagnet mounted on said tube for applying a magnetic field across a blood vessel to induce an electric signal in the blood flowing therethrough; said electromagnet comprising: an electrically conductive coil having an interior wall defining an open central portion; and an electrically nonconductive magnetic core substantially filling said open central portion of said coil and conforming to and being in intimate and continuous contact with said interior wall of said coil and a portion of the exterior surface of said tube; said core comprising a hardened resin having ferromagnetic particles suspended therein; and signal measuring means operatively connected to said tube for measuring the magnitude of the electric signal induced in the blood flowing through the blood vessel.
 2. A blood flowmeter in which a magnetic field is induced in a blood vessel by means of an electromagnet to induce an electrical signal when blood flows through said blood vessel, the improvement which comprises a hollow cylindrical tube adapted to fit around the blood vessel, an electromagnet mounted on said tube, for applying a magnetic field across said tube, said electromagnet comprising an electrically conductive coil having an interior walL defining an open central portion; and an electrically nonconductive magnetic core substantially filling said open central portion of said coil, and conforming to and being in intimate and continuous contact with said interior wall of said coil, said core comprising a resin having therethrough magnetic particles suspended therein.
 3. A lumen for a blood flowmeter, said lumen comprising an insulated hollow cylindrical tube adapted to fit around a blood vessel, an electromagnet mounted on said tube to apply a magnetic field across said tube, said electromagnet comprising an electrically conductive coil having an interior wall defining an open central portion and an electrically nonconductive magnetic core substantially filling said open central portion of said coil and conforming to and being in intimate and continuous contact with said interior wall of said coil, said core comprising a hardened resin with magnetic particles suspended therein. 